Book Review: Dirt: The Erosion of Civilizations

CVN member Tony de Castro submitted this book review, which he wrote and previously published elsewhere, with this comment: “This title is a few years old now, but the issues have not changed at all and the problems are, in fact, becoming more acute.”


Dirt: The Erosion of Civilizations

By David R. Montgomery

2nd edition, 2012
University of California Press
296 pages, paperback
ISBN-13 ‏: ‎ 978-0520272903

Taking a composting class a few years ago, I remember the instructor commenting that one person in a previous class had dropped out very early after looking at a compost pile because the organic matter was, according to the student, “dirty and smelly”. In North America we often use the word “dirt” as a generic term to describe a range of types of earth or soil. This perhaps implies in the minds of some that we somehow consider soil not valuable or clean, something to be avoided. And children in large urban environments, where most surfaces are paved over, can sometimes spend months without being exposed to soil and its by-products. And yet, without soil, human life would not be possible on this planet.

Soil is “the mixture of minerals, organic matter, gases, liquids, and myriad organisms that together support plant life” [Wikipedia]. David R. Montgomery, a geologist from the University of Washington tells us all we want to know about soil. In his book Dirt: The Erosion of Civilizations Montgomery argues that throughout history, once societies had more people than their land base could feed, they eventually crashed. Sometimes they could buy some time by colonizing other people’s land, but this often only delayed the inevitable. So the quality and availability of topsoil seems to determine, to a great extent, the lifespan of most cultures that can’t control other people’s land, or that don’t have resources to import large volumes of food from abroad.

When humans invented agriculture (about 10,000 to 15,000 years ago), the majority of people in agricultural societies worked on the land to support a small elite that controlled the planting, harvesting, storage and distribution of crops. In the US today less than 1% of the population still works in agriculture to produce the bulk of the food for the rest of the population. These percentages are fairly similar in Canada and in most other industrialized countries.

While the population of the planet keeps increasing, the amount of productive farmland has been declining at least for the last 40 years. This is the result of multiple factors, among which we can list soil erosion brought about by deforestation and poor farming practices, soil exhaustion from overuse of the same tracts of land, salinity from unsuitable irrigation techniques, over-reliance on pesticides and chemical fertilizers, and paving over some of the best farmland on valley bottoms to allow cities to continue expanding outwards. The end result is that, in many countries, crop yields per square kilometer have been going down. In the past farmers would just move, cut down more forest and start planting again. We are now running out of room. The planet has fewer and fewer “virgin” lands where we can repeat the mistakes of previous generations.

Most societies view oil as a “strategic” commodity over which countries are prepared to go to war. Meanwhile, soil barely registers as an important asset. When did anybody last invade their neighbour to preserve the quality of the topsoil in the region? And yet, more countries are beginning to figure out that while soil is one of our least valued assets, we can’t survive without it. Some countries are trying to buy time by acquiring farming land on other continents. When you don’t have enough healthy topsoil and clean water to grow crops, you buy it. Countries like China, Saudi Arabia, South Korea, and India are buying large tracts of farmland in Africa to grow crops and send the food back home. Two-thirds of the land being purchased is in Africa. South American countries are also noticing more expressions of interest from potential purchasers.

Montgomery does a great job of giving us an overview of the biology and geology of soil. Earthworms play an essential role in the formation and health of soil. Through their digestion and locomotion, worms slowly break up, mix and distribute soil across the top layers of your average field. They do this by mixing granules derived from the erosion of rocks with recycled organic matter from the decay of plants. The acids found in the intestines of worms help to dissolve grains of rock into smaller and smaller sizes. The castings of worms, made up of these traces of minerals and digested animal and vegetable matter become eventually the topsoil we see when we walk around a healthy field. They are also assisted in this by an army of bacteria, fungi and other life forms, which form a true biochemical web of soil makers.

The status of soil is a balance between weathering and erosion. Weathering is the physical and biochemical process by which larger rocks are broken down into smaller and smaller granules. Erosion is the set of physical processes that strip topsoil from a field and move it downhill via rainfall or gravity, or far away via wind forces. If more soil is produced than is eroded, then the topsoil layer thickens. If more erosion than soil creation takes place, then topsoil thins out. Eventually soil establishes a balance between erosion and new soil creation. The soil thickness we see in a particular area is the result of this competition between soil creation and erosion.

What determines how healthy topsoil is? Some of the main factors are the topography of the area (steep slopes versus flat valley bottoms), the local geology (which determines if soils are sandy, clay-rich and so on), the amount of rain, snow and seasonal temperatures, the presence of farm animals, the type of farming conducted in the area, the type of vegetation present, logging practices, and the use of pesticides and other chemicals.

Rich topsoil maintains itself by supporting plant communities that eventually return organic matter back to the soil. This in turn supports other new plants and animals in the area, producing a virtuous cycle where soil recycles dead materials to create new life. Without this topsoil, the earthworms, the microbes that live in the soil and all the plants and animals that live in the area, you can’t grow food and you can’t support humans and farm animals.

How can farming practices preserve and improve soil? Tilling the soil on a regular basis can kill large soil dwelling animals and earthworms. Pesticides kill microbes. Monocultures reduce biodiversity and encourage the spread of specific pathogens and crop-eating insects. Farming on slopes and clearcutting encourage erosion and landslides. On the other hand, increasing the amount of organic matter in the soil binds soil particles together, resisting erosion. Encouraging the growth of plant cover creates a network of roots that stabilizes the soil and retains moisture. Terracing sloped land slows down runoff and reduces erosion. No-till or low-till methods also minimize soil disturbance. Mulching the soil and inter-planting crops can provide more ground cover and minimize erosion.

Soil that starts losing its top layer becomes less and less productive, as the deeper you go, the less fertile the soil is. Most of the planet has soil that is susceptible to erosion if clearcut or tilled repeatedly. In addition, the organic matter in soil declines under continued cultivation, as it oxidizes when exposed to air. So the more often the soil is plowed, the faster it loses organic content and the easier it is to erode because of wind, rain and domestic animals. So the trick is to manage the rate of soil erosion so that soil is created at least just as fast as it is being eroded. The US Department of Agriculture has estimated that it can take up to 500 years to create an inch of topsoil. This can be lost in less than a decade if the wrong agricultural practices are used.

Montgomery also gives us a good overview of the link between the type of agricultural practices we are engaging in, their effects on topsoil, and likely future scenarios given human population growth trends. The human population on Earth is increasing steadily. The amount of fertile topsoil is limited and going down in certain parts of the world. Estimating how many people our planet can support relies on uncertain assumptions about the agricultural technology we are likely to have as years go by, the quality of life we are satisfied with, the long-term effects of global warming, and the amount of biodiversity we want or need to sustain ecosystems.

At the moment we are using about 40% of the Earth’s total photosynthetic productivity to sustain the human race. If we used 100% of that photosynthetic productivity to benefit only us and got rid of all other lifeforms that don’t directly feed us, we could support about 15 billion people. Of course, a world tailored only for humans is total science fiction from a technical point of view. We can’t survive without bees to pollinate our crops and all the other millions of life forms that contribute to our welfare. And, in any case, who would want to live in such a world?

Predicting the world population down the road is a notoriously difficult job. There are so many variables to consider, and every time one looks at the data it is easy to get different numbers based on different assumptions. The UN has estimates based on “low”, “medium” and “high” projections. A few years ago calculations had the global population peaking at 9 billion by 2070 and then easing to 8.4 billion by 2100. At the moment we have about 8 billion people. Recently the UN revised these numbers. The population is now expected to rise to 9.7 billion by 2050 and continue to 10.4 billion by 2100. So how we will feed everybody on this planet with a limited amount of topsoil is an interesting question. And 2100 is not that far away. Quite a few people born this week will be alive in 2100.

So what are the implications of all of this for us? Montgomery argues that large scale industrial farmers, who quite often use conventional agricultural techniques and plant monocultures, are basically trying to maximize short to medium term profits without giving much thought to long term soil erosion. It is easy to see the world from the perspective of these farmers. They often have to lease land, service debt on very expensive machinery, pay staff, buy pesticides and fertilizers, buy insurance and so on. Having said that, for many of them farming is a business, not a way of life. If the project does not produce enough returns, once the soil is exhausted, they just move on to lease another plot of land or move on to another type of business. The long-term health of the soil and wanting to see their kids stay in farming may just not enter into the equation.

Peasant farmers in developing countries sometimes contribute to soil erosion for different reasons. They often only have access to plots of land that are too small to feed their families. So, despite their best efforts, they overexploit the soil until crop yields start to crash. Depending on where they live and whether there is public land nearby, some of them just move further into the forest or jungle and clear another patch of land to start again. But given that these soils are often of very poor quality, the topsoil is again exhausted within two or three seasons and they have to move again. As this happens, the portion of undisturbed forest or jungle keeps shrinking, creating a different set of problems for the animals that live in that ecosystem, and making it easier for heavy rains to just wash everything downhill leaving a lunar landscape behind.

If we are facing a global scenario where the human population of this planet is increasing while the amount of good topsoil is decreasing, what are our options? Well, if we want to avoid hunger we need to make soil stewardship a priority. This is not a very “sexy” topic and probably hardly anybody gives it much thought, but without healthy topsoil, clean water, and a new generation of youngsters who want to go into farming, feeding everybody is just not going to happen. Some areas of the world will manage fine, but many others will not have enough agricultural resources to feed themselves. Unless we feel comfortable watching millions of people have less and less access to affordable food in the coming decades, Montgomery argues that we can’t view agriculture just like any other business. History has taught us that past civilizations grew and prospered as long as there was new land to plow or the soil remained productive through proper stewardship. Any combination of economic upheaval, climate extremes, and falling food production can bring down a society. Interestingly, population growth in many parts of the world is coming at a time when climate events (often droughts and floods) are creating a lot of political instability. When people are hungry, they often get angry.

Now, you can probably already hear the optimists telling us that there is nothing to worry about. Science will somehow save us. Advances in GMO technology, hydroponics, and better pesticides and fertilizers will save the day. While that may be the case for a few decades in a few countries, the bulk of the world’s farmers in places like Africa, India and many other countries just do not have the income or the technology to practice high-tech agriculture. In fact, in places like India, the number of suicides of farmers has reached unacceptable levels. In 2012, for example, over 13,000 Indian farmers committed suicide. Causes vary, but high debt loads they couldn’t hope to repay was cited as one of the principal reasons. It would thus be unrealistic to expect that this type of farmer would want to consider even higher debt commitments to finance even more technologically complex agriculture. And GMO companies are not about to start giving away their products for free indefinitely for the good of humankind.

Montgomery finishes his book by giving us some short to medium term alternatives. We can start fighting over the remaining pool of good farmland as the world population increases and soil fertility declines. We can maintain blind faith in some future technological miracle that will save us by increasing crop yields to match population numbers, or we can limit population growth while protecting the quality of our remaining soil.

Montgomery tells us that the best agricultural land is already under production. The areas still not exploited are of marginal quality and will be exhausted in a few decades. Moving into those areas is more of a delaying tactic than a long term solution. In the second half of the 20th century, food production per hectare doubled thanks to a sevenfold increase in the use of nitrogen fertilizers and a threefold increase in phosphorus use. This strategy will no longer work in the future, as plants can only absorb so much nitrogen and phosphorus. If you keep adding more, the plant just does not absorb it.

Our long term choices are stark. We can, according to Montgomery, have a type of agriculture where we try to force the land to adapt to our technology, or we can have an agriculture where we adapt to the type of soil and landscape we have. Our industrial agriculture for the last century has been based on chemistry and genetics. Future options will need to be based on biology and ecology. Agricultural methods that speed up the loss of topsoil will accelerate the collapse of societies. Are we ready for the change in mindset required to redesign agriculture? Or do we just want to drive to the supermarket tomorrow looking for cheap food without caring where it comes from and how it was produced?

Tony notes that this book has the following ratings at the indicated websites:
– 3.96 stars out of 5 at goodreads.com
– 4.8 stars out of 5 at amazon.com